1. Field of the Invention
The invention relates generally to exercise equipment. Specifically, this invention relates to dumbbells and barbells, and methods for making same.
2. Background Art
Dumbbells and barbells have been used for building body strength and for general fitness, strength and endurance training, and physical rehabilitation. Typically, dumbbells and barbells have elongated cylindrical bars or handles with disk-shaped weight heads (or weight plates) placed at both ends.
FIG. 1 shows a schematic illustrating a typical dumbbell 10, which comprises a handle 11 and two weight plates 12a and 12b. The handles 11 and/or weight plates 12a and 12b may be coated with a resilient material, such as vinyl, urethane, or rubber, to prevent marring of floors and other surfaces. Such coatings also help alleviate the noise that otherwise would result from the banging of the dumbbells or barbells against other equipment.
Dumbbells and barbells are often used in a rough manner and are commonly dropped on the floor or banged against other equipment. Durability and safety are therefore essential requirements for dumbbells and barbells, particularly for devices used in commercial settings, where heavy use is expected. Therefore, the bars or handles 10 are typically made of strong and durable materials, such as carbon steel, stainless steel, cast iron, and the like, and the weight plates 12a and 12b are typically made of durable and heavy materials, such as steel, cast iron, concrete, and others. Among these materials, steel and cast iron are among the most frequently used because they are strong and durable.
Dumbbells and barbells may be categorized as fixed-weight or adjustable-weight dumbbells or barbells. Fixed-weight dumbbells and barbells have weight plates that are permanently or semi-permanently fixed—i.e., the weight plates in fixed-weight dumbbells or barbells are not intended to be changed by users. On the other hand, in adjustable dumbbells and barbells, weight plates are attached in a removable manner and may be added and removed by the users as needed.
For fixed-weight dumbbells or barbells, the attachment of weight plates to handle bars may be accomplished by bolts and nuts or by welding. The use bolts or nuts has a number of drawbacks because dumbbells and barbells often endure multiple types of mechanical stresses, shocks, and vibrations during the course of a workout as they are haphazardly dropped and tossed about. These mechanical stresses, shocks, and vibrations can cause the bolts holding the weight plates on the bar or handle to gradually work themselves loose over time and back out, rendering the dumbbells or barbells potentially unsafe. Therefore, permanent attachments by welding the weight plates to the handle bars is often preferred.
Permanently attached dumbbells or barbells are typically made of cast iron or steel, and in some cases the entire handle and weighted plates may be formed of a single piece of material, such as steel. Although dumbbells and barbells made entirely of steel may be desirable, they are far more expensive, as compared to those made of cast iron. On the other hand, cast iron is more brittle than steel, and it is undesirable to make the dumbbells or barbells entirely out of cast iron. Therefore, combinations of steel bars and cast iron weight plates seem to present a good compromise that takes advantage of different material properties and reduced costs.
Although steel and cast iron may be welded together, the steel and cast iron welds may be brittle and weak due to the different properties of cast iron and steel, such as different melting temperatures, different hardness, and different thermal expansion coefficients. Therefore, there remains a need for improved methods for making dumbbells and barbells that remain secure and safe.